Method and system for display of cardiac event intervals in a resynchronization pacemaker

ABSTRACT

A cardiac rhythm management system that includes a pacemaker configured for biventricular pacing and an external programmer with an associated display for displaying electrogram data and markers representing ventricular events. Associated with each marker are intraventricular intervals designed to relate information to a user in a manner suited for ventricular resynchronization pacing.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a division of U.S. patent application Ser. No.09/748,724, filed on Dec. 26, 2000, now U.S. Pat. No. 6,957,100, thespecification of which is incorporated herein by reference.

FIELD OF THE INVENTION

This invention pertains to cardiac rhythm management devices such aspacemakers. In particular, the invention relates to methods and systemsfor the display of data collected by such devices.

BACKGROUND

Cardiac pacemakers are cardiac rhythm management devices that provideelectrical stimulation in the form of pacing pulses to selected chambersof the heart. (As the term is used herein, a pacemaker is any cardiacrhythm management device that performs cardiac pacing, includingimplantable cardioverter/defibrillators having a pacing functionality.)Cardiac rhythm management devices are usually implanted subcutaneouslyon a patient's chest and have leads threaded intravenously into theheart to connect the device to electrodes used for sensing and pacing,the electrodes being disposed in proximity to selected chambers of theheart. Pacemakers typically have a programmable electronic controllerthat causes the pacing pulses to be output in response to lapsed timeintervals and sensed intrinsic cardiac activity.

The most common condition for which pacemakers are used is in thetreatment of bradycardia, where the ventricular rate is too slow. Iffunctioning properly, a pacemaker makes up for the heart's inability topace itself at an appropriate rhythm in order to meet metabolic demandby enforcing a minimum heart rate. Pacing therapy can also be used inthe treatment of congestive heart failure (CHF). It has also been shownthat some CHF patients suffer from intraventricular and/orinterventricular conduction defects such that their cardiac outputs canbe increased by improving the synchronization of right and leftventricular contractions with electrical stimulation, referred to hereinas ventricular resynchronization therapy.

Modern pacemakers also typically have the capability to communicate datavia a data link with an external programming device. Such data istransmitted to the pacemaker in order to program its mode of operationas well as define other operating parameters. Data is also transmittedfrom the pacemaker which can be used to verify the operating parametersas well as inform the clinician as to the condition of both thepacemaker and the patient. Among the most useful data which maytypically be telemetered from the pacemaker are electrogramsrepresenting the time sequence of sensing and pacing events. The presentinvention is concerned with informatively displaying such electrogramdata.

SUMMARY OF THE INVENTION

The present invention relates to a method and system for displaying timeintervals between cardiac events on an external programmer display basedupon data transmitted from a pacemaker operating in a resychronizationpacing mode. In such a mode, one heart chamber may be designated as arate chamber with the contralateral chamber designated as thesynchronized chamber. Sensing/pacing channels are provided for eachchamber, and one or both of the chambers are paced in a mode based uponsenses and paces occurring in the rate chamber. For example, in abiventricular resynchronization pacing mode, paces may be outputsynchronously to either both ventricles or only one ventricle based uponright ventricular senses. In accordance with the invention, markersrepresenting cardiac sensing and pacing events are displayed spacedapart in accordance with their time sequence. Each marker indicateswhether the event is a sense or a pace and in which chamber the eventoccurred. Associated with each marker is also an indication of aintraventricular interval for the event, which is the time intervalmeasured from another ventricular event.

In one embodiment, where the pacemaker is operating in a biventricularresynchronization pacing mode based upon right ventricular senses,markers for both right and left ventricular events are displayed withtime intervals measured from the previous right ventricular event. Inthe case of a left ventricle-only pacing mode, right and leftventricular event markers are displayed with time intervals measuredfrom the nearest preceding right ventricular sense or left ventricularpace. In another embodiment for biventricular resynchronization pacing,left ventricular event markers are displayed with time intervalsmeasured from the nearest right ventricular event, which may precede orfollow the left ventricular event marker as indicated by the intervalbeing positive or negative, respectively. In a modification to thisembodiment, the absolute value of the interval is displayed in alignmentwith the marker representing the later of either the left ventricular orright ventricular event.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram of a cardiac rhythm management system thatincludes a microprocessor-based pacemaker and external programmer.

FIGS. 2A through 2D show timelines of events in the right and leftventricular channels of a biventricular pacemaker and a sequence ofmarkers indicating sensing and pacing events and intraventricularintervals.

DESCRIPTION OF THE INVENTION

It is useful for a clinician to be able to monitor the operation of apacemaker with an external programmer by viewing a representation of anelectrogram indicating a temporal sequence of sensing and pacing events.In a pacemaker configured to pace either ventricle or both ventricles inorder to deliver ventricular resynchronization therapy, events occurringin both the right and left ventricular sensing/pacing channels should bedisplayed. Such a pacemaker may pace the heart in a number of differentpacing modes, including modes in which one ventricle is paced based uponsenses in the other ventricle. The present invention is a scheme forpresenting this information along with time intervals betweenventricular events in a clear and concise manner across the differentpacing modes that the pacemaker may employ.

1. Hardware Platform

Pacemakers are typically implanted subcutaneously on a patient's chestand have leads threaded intravenously into the heart to connect thedevice to electrodes used for sensing and pacing. A programmableelectronic controller causes the pacing pulses to be output in responseto lapsed time intervals and sensed electrical activity (i.e., intrinsicheart beats not as a result of a pacing pulse). Pacemakers senseintrinsic cardiac electrical activity by means of internal electrodesdisposed near the chamber to be sensed. A depolarization wave associatedwith an intrinsic contraction of the atria or ventricles that isdetected by the pacemaker is referred to as an atrial sense orventricular sense, respectively. In order to cause such a contraction inthe absence of an intrinsic beat, a pacing pulse (either an atrial paceor a ventricular pace) with energy above a certain pacing threshold isdelivered to the chamber.

FIG. 1 shows a system diagram of a microprocessor-based pacemakerphysically configured with sensing and pacing channels for both atriaand both ventricles. The controller 10 of the pacemaker is amicroprocessor which communicates with a memory 12 via a bidirectionaldata bus. The memory 12 typically comprises a ROM (read-only memory) forprogram storage and a RAM (random-access memory) for data storage. Thepacemaker has atrial sensing and pacing channels comprising electrode 34a–b, leads 33 a–b, sensing amplifiers 31 a–b, pulse generators 32 a–b,and atrial channel interfaces 30 a–b which communicate bidirectionallywith microprocessor 10. The device also has ventricular sensing andpacing channels for both ventricles comprising electrodes 24 a–b, leads23 a–b, sensing amplifiers 21 a–b, pulse generators 22 a–b, andventricular channel interfaces 20 a–b. In the figure, “a” designates oneventricular or atrial channel and “b” designates the channel for thecontralateral chamber. In this embodiment, a single electrode is usedfor sensing and pacing in each channel, known as a unipolar lead. Otherembodiments may employ bipolar leads which include two electrodes foroutputting a pacing pulse and/or sensing intrinsic activity. The channelinterfaces 20 a–b and 30 a–b include analog-to-digital converters fordigitizing sensing signal inputs from the sensing amplifiers andregisters which can be written to by the microprocessor in order tooutput pacing pulses, change the pacing pulse amplitude, and adjust thegain and threshold values for the sensing amplifiers. An exertion levelsensor 330 (e.g., an accelerometer or a minute ventilation sensor)enables the controller to adapt the pacing rate in accordance withchanges in the patient's physical activity. A telemetry interface 40 isalso provided for communicating with an external programmer 500 whichhas an associated display 510. A pacemaker incorporating the presentinvention may possess all of the components in FIG. 1 and beprogrammable so as to operate in a number of different modes, or it mayhave only those components necessary to operate in a particular mode.

The controller 10 controls the overall operation of the device inaccordance with programmed instructions stored in memory. The controller10 interprets sense signals from the sensing channels and controls thedelivery of paces in accordance with a pacing mode. The sensingcircuitry of the pacemaker generates atrial and ventricular sensesignals when voltages sensed by the electrodes exceed a specifiedthreshold. The sense signals from each channel, together with the pacesdelivered, represent an electrogram that can either be transmitted viathe telemetry link to an external programmer or stored for latertransmission. The operation of the pacemaker and the patient's cardiacactivity may thus be observed in real-time or over a selected historicalperiod. In the latter case, the recording of an electrogram may betriggered by the detection of certain events or conditions such as anarrhythmia.

2. Bradycardia Pacing Modes

Bradycardia pacing modes refer to pacing algorithms used to pace theatria and/or ventricles when the intrinsic atrial and/or ventricularrate is inadequate due to, for example, AV conduction blocks or sinusnode dysfunction. Such modes may either be single-chamber pacing, whereeither an atrium or a ventricle is paced, or dual-chamber pacing inwhich both an atrium and a ventricle are paced. The modes are generallydesignated by a letter code of three positions where each letter in thecode refers to a specific function of the pacemaker. The first letterrefers to which heart chambers are paced and which may be an A (foratrium), a V (for ventricle), D (for both chambers), or O (for none).The second letter refers to which chambers are sensed by the pacemaker'ssensing channels and uses the same letter designations as used forpacing. The third letter refers to the pacemaker's response to a sensedP wave from the atrium or an R wave from the ventricle and may be an I(for inhibited), T (for triggered), D (for dual in which both triggeringand inhibition are used), and O (for no response). Modern pacemakers aretypically programmable so that they can operate in any mode which thephysical configuration of the device will allow. Additional sensing ofphysiological data allows some pacemakers to change the rate at whichthey pace the heart in accordance with some parameter correlated tometabolic demand. Such pacemakers are called rate-adaptive pacemakersand are designated by a fourth letter added to the three-letter code, R.

Pacemakers can enforce a minimum heart rate either asynchronously orsynchronously. In asynchronous pacing, the heart is paced at a fixedrate irrespective of intrinsic cardiac activity. There is thus a riskwith asynchronous pacing that a pacing pulse will be deliveredcoincident with an intrinsic beat and during the heart's vulnerableperiod which may cause fibrillation. Most pacemakers for treatingbradycardia today are therefore programmed to operate synchronously in aso-called demand mode where sensed cardiac events occurring within adefined interval either trigger or inhibit a pacing pulse. Inhibiteddemand pacing modes utilize escape intervals to control pacing inaccordance with sensed intrinsic activity. In an inhibited demand mode,a pacing pulse is delivered to a heart chamber during a cardiac cycleonly after expiration of a defined escape interval during which nointrinsic beat by the chamber is detected. If an intrinsic beat occursduring this interval, the heart is thus allowed to “escape” from pacingby the pacemaker. Such an escape interval can be defined for each pacedchamber. For example, a ventricular escape interval can be definedbetween ventricular events so as to be restarted with each ventricularsense or pace. The inverse of this escape interval is the minimum rateat which the pacemaker will allow the ventricles to beat, sometimesreferred to as the lower rate limit (LRL).

In atrial tracking pacemakers (i.e., VDD or DDD mode), anotherventricular escape interval is defined between atrial and ventricularevents, referred to as the atrio-ventricular interval (AVI). Theatrio-ventricular interval is triggered by an atrial sense or pace andstopped by a ventricular sense or pace. A ventricular pace is deliveredupon expiration of the atrio-ventricular interval if no ventricularsense occurs before. Atrial-tracking ventricular pacing attempts tomaintain the atrio-ventricular synchrony occurring with physiologicalbeats whereby atrial contractions augment diastolic filling of theventricles. If a patient has a physiologically normal atrial rhythm,atrial-tracking pacing also allows the ventricular pacing rate to beresponsive to the metabolic needs of the body.

A pacemaker can also be configured to pace the atria on an inhibiteddemand basis. An atrial escape interval is then defined as the maximumtime interval in which an atrial sense must be detected after aventricular sense or pace before an atrial pace will be delivered. Whenatrial inhibited demand pacing is combined with atrial-triggeredventricular demand pacing (i.e., DDD mode), the lower rate limitinterval is then the sum of the atrial escape interval and theatrio-ventricular interval.

Another type of synchronous pacing is atrial-triggered orventricular-triggered pacing. In this mode, an atrium or ventricle ispaced immediately after an intrinsic beat is detected in the respectivechamber. Triggered pacing of a heart chamber is normally combined withinhibited demand pacing so that a pace is also delivered upon expirationof an escape interval in which no intrinsic beat occurs. Such triggeredpacing may be employed as a safer alternative to asynchronous pacingwhen, due to far-field sensing of electromagnetic interference fromexternal sources or skeletal muscle, false inhibition of pacing pulsesis a problem. If a sense in the chamber's sensing channel is an actualdepolarization and not a far-field sense, the triggered pace isdelivered during the chamber's physiological refractory period and is ofno consequence.

Finally, rate-adaptive algorithms may be used in conjunction withbradycardia pacing modes. Rate-adaptive pacemakers modulate theventricular and/or atrial escape intervals based upon measurementscorresponding to physical activity. Such pacemakers are applicable tosituations in which atrial tracking modes cannot be used. In arate-adaptive pacemaker operating in a ventricular pacing mode, forexample, the LRL is adjusted in accordance with exertion levelmeasurements such as from an accelerometer or minute ventilation sensorin order for the heart rate to more nearly match metabolic demand. Theadjusted LRL is then termed the sensor-indicated rate.

3. Cardiac Resynchronization Therapy

Cardiac resynchronization therapy is pacing stimulation applied to oneor more heart chambers in a manner that restores or maintainssynchronized bilateral contractions of the atria and/or ventricles andthereby improves pumping efficiency. Certain patients with conductionabnormalities may experience improved cardiac synchronization withconventional single-chamber or dual-chamber pacing as described above.For example, a patient with left bundle branch block may have a morecoordinated contraction of the ventricles with a pace than as a resultof an intrinsic contraction. In that sense, conventional bradycardiapacing of an atrium and/or a ventricle may be considered asresynchronization therapy. Resynchronization pacing, however, may alsoinvolve pacing both ventricles and/or both atria in accordance with asynchronized pacing mode as described below. A single chamber may alsobe resynchronized to compensate for intra-atrial or intra-ventricularconduction delays by delivering paces to multiple sites of the chamber.

It is advantageous to deliver resynchronization therapy in conjunctionwith one or more synchronous bradycardia pacing modes, such as aredescribed above. One atrial and/or one ventricular pacing sites aredesignated as rate sites, and paces are delivered to the rate sitesbased upon pacing and sensed intrinsic activity at the site inaccordance with the bradycardia pacing mode. In a single-chamberbradycardia pacing mode, for example, one of the paired atria or one ofthe ventricles is designated as the rate chamber. In a dual-chamberbradycardia pacing mode, either the right or left atrium is selected asthe atrial rate chamber and either the right or left ventricle isselected as the ventricular rate chamber. The heart rate and the escapeintervals for the pacing mode are defined by intervals between sensedand paced events in the rate chambers only. Resynchronization therapymay then be implemented by adding synchronized pacing to the bradycardiapacing mode where paces are delivered to one or more synchronized pacingsites in a defined time relation to one or more selected sensing andpacing events that either reset escape intervals or trigger paces in thebradycardia pacing mode. Multiple synchronized sites may be pacedthrough multiple synchronized sensing/pacing channels, and the multiplesynchronized sites may be in the same or different chambers as the ratesite.

In bilateral synchronized pacing, which may be either biatrial orbiventricular synchronized pacing, the heart chamber contralateral tothe rate chamber is designated as a synchronized chamber. For example,the right ventricle may be designated as the rate ventricle and the leftventricle designated as the synchronized ventricle, and the paired atriamay be similarly designated. Each synchronized chamber is then paced ina timed relation to a pace or sense occurring in the contralateral ratechamber.

One synchronized pacing mode may be termed offset synchronized pacing.In this mode, the synchronized chamber is paced with a positive,negative, or zero timing offset as measured from a pace delivered to itspaired rate chamber, referred to as the synchronized chamber offsetinterval. The offset interval may be zero in order to pace both chamberssimultaneously, positive in order to pace the synchronized chamber afterthe rate chamber, or negative to pace the synchronized chamber beforethe rate chamber. One example of such pacing is biventricular offsetsynchronized pacing where both ventricles are paced with a specifiedoffset interval. The rate ventricle is paced in accordance with asynchronous bradycardia mode which may include atrial tracking, and theventricular escape interval is reset with either a pace or a sense inthe rate ventricle. (Resetting in this context refers to restarting theinterval in the case of an LRL ventricular escape interval and tostopping the interval in the case of an AVI.) Thus, a pair ofventricular paces are delivered after expiration of the AVI escapeinterval or expiration of the LRL escape interval, with ventricularpacing inhibited by a sense in the rate ventricle that restarts the LRLescape interval and stops the AVI escape interval. In this mode, thepumping efficiency of the heart will be increased in some patients bysimultaneous pacing of the ventricles with an offset of zero. However,it may be desirable in certain patients to pace one ventricle before theother in order to compensate for different conduction velocities in thetwo ventricles, and this may be accomplished by specifying a particularpositive or negative ventricular offset interval.

Another synchronized mode is triggered synchronized pacing. In one typeof triggered synchronized pacing, the synchronized chamber is pacedafter a specified trigger interval following a sense in the ratechamber, while in another type the rate chamber is paced after aspecified trigger interval following a sense in the synchronizedchamber. The two types may also be employed simultaneously. For example,with a trigger interval of zero, pacing of one chamber is triggered tooccur in the shortest time possible after a sense in the other chamberin order to produce a coordinated contraction. (The shortest possibletime for the triggered pace is limited by a sense-to-pace latency perioddictated by the hardware.) This mode of pacing may be desirable when theintra-chamber conduction time is long enough that the pacemaker is ableto reliably insert a pace before depolarization from one chamber reachesthe other. Triggered synchronized pacing can also be combined withoffset synchronized pacing such that both chambers are paced with thespecified offset interval if no intrinsic activity is sensed in the ratechamber and a pace to the rate chamber is not otherwise delivered as aresult of a triggering event. A specific example of this mode isventricular triggered synchronized pacing where the rate andsynchronized chambers are the right and left ventricles, respectively,and a sense in the right ventricle triggers a pace to the left ventricleand/or a sense in the left ventricle triggers a pace to the rightventricle.

As with other synchronized pacing modes, the rate chamber in a triggeredsynchronized pacing mode can be paced with one or more synchronousbradycardia pacing modes. If the rate chamber is controlled by atriggered bradycardia mode, a sense in the rate chamber sensing channel,in addition to triggering a pace to the synchronized chamber, alsotriggers an immediate rate chamber pace and resets any rate chamberescape interval. The advantage of this modal combination is that thesensed event in the rate chamber sensing channel might actually be afar-field sense from the synchronized chamber, in which case the ratechamber pace should not be inhibited. In a specific example, the rightand left ventricles are the rate and synchronized chambers,respectively, and a sense in the right ventricle triggers a pace to theleft ventricle. If right ventricular triggered pacing is also employedas a bradycardia mode, both ventricles are paced after a rightventricular sense has been received to allow for the possibility thatthe right ventricular sense was actually a far-field sense of leftventricular depolarization in the right ventricular channel. If theright ventricular sense were actually from the right ventricle, theright ventricular pace would occur during the right ventricle'sphysiological refractory period and cause no harm.

As mentioned above, certain patients may experience some cardiacresynchronization from the pacing of only one ventricle and/or oneatrium with a conventional bradycardia pacing mode. It may be desirable,however, to pace a single atrium or ventricle in accordance with apacing mode based upon senses from the contralateral chamber. This mode,termed synchronized chamber-only pacing, involves pacing only thesynchronized chamber based upon senses from the rate chamber. One way toimplement synchronized chamber-only pacing is to pseudo-pace the ratechamber whenever the synchronized chamber is paced before the ratechamber is paced, such that the pseudo-pace inhibits a rate chamber paceand resets any rate chamber escape intervals. Such pseudo-pacing can becombined with the offset synchronized pacing mode using a negativeoffset to pace the synchronized chamber before the rate chamber and thuspseudo-pace the rate chamber, which inhibits the real scheduled ratechamber pace and resets the rate chamber pacing escape intervals. Oneadvantage of this combination is that sensed events in the rate chamberwill inhibit the synchronized chamber-only pacing, which may benefitsome patients by preventing pacing that competes with intrinsicactivation (i.e., fusion beats). Another advantage of this combinationis that rate chamber pacing can provide backup pacing when in asynchronized chamber-only pacing mode, such that when the synchronizedchamber pace is prevented, for example to avoid pacing during thechamber vulnerable period following a prior contraction, the ratechamber will not be pseudo-paced and thus will be paced upon expirationof the rate chamber escape interval. Synchronized chamber-only pacingcan be combined also with a triggered synchronized pacing mode, inparticular with the type in which the synchronized chamber is triggeredby a sense in the rate chamber. One advantage of this combination isthat sensed events in the rate chamber will trigger the synchronizedchamber-only pacing, which may benefit some patients by synchronizingthe paced chamber contractions with premature contralateral intrinsiccontractions.

An example of synchronized chamber-only pacing is left ventricle-onlysynchronized pacing where the rate and synchronized chambers are theright and left ventricles, respectively. Left ventricle-onlysynchronized pacing may be advantageous where the conduction velocitieswithin the ventricles are such that pacing only the left ventricleresults in a more coordinated contraction by the ventricles than withconventional right ventricular pacing or biventricular pacing. Leftventricle-only synchronized pacing may be implemented in inhibiteddemand modes with or without atrial tracking, similar to biventricularpacing. A left ventricular pace is then delivered upon expiration of theAVI escape interval or expiration of the LRL escape interval, with leftventricular pacing inhibited by a right ventricular sense that restartsthe LRL escape interval and stops the AVI escape interval.

In the synchronized modes described above, the rate chamber issynchronously paced with a mode based upon detected intrinsic activityin the rate chamber, thus protecting the rate chamber against pacesbeing delivered during the vulnerable period. In order to providesimilar protection to a synchronized chamber or synchronized pacingsite, a synchronized chamber protection period (SCPP) may be provided.(In the case of multi-site synchronized pacing, a similar synchronizedsite protection period may be provided for each synchronized site.) TheSCPP is a programmed interval which is initiated by sense or paceoccurring in the synchronized chamber during which paces to thesynchronized chamber are inhibited. For example, if the right ventricleis the rate chamber and the left ventricle is the synchronized chamber,a left ventricular protection period LVPP is triggered by a leftventricular sense which inhibits a left ventricular pace which wouldotherwise occur before the escape interval expires. The SCPP may beadjusted dynamically as a function of heart rate and may be differentdepending upon whether it was initiated by a sense or a pace. The SCPPprovides a means to inhibit pacing of the synchronized chamber when apace might be delivered during the vulnerable period or when it mightcompromise pumping efficiency by pacing the chamber too close to anintrinsic beat. In the case of a triggered mode where a synchronizedchamber sense triggers a pace to the synchronized chamber, the pacingmode may be programmed to ignore the SCPP during the triggered pace.Alternatively, the mode may be programmed such that the SCPP starts onlyafter a specified delay from the triggering event, which allowstriggered pacing but prevents pacing during the vulnerable period.

In the case of synchronized chamber-only synchronized pacing, asynchronized chamber pace may be inhibited if a synchronized chambersense occurs within a protection period prior to expiration of the ratechamber escape interval. Since the synchronized chamber pace isinhibited by the protection period, the rate chamber is not pseudo-pacedand, if no intrinsic activity is sensed in the rate chamber, it will bepaced upon expiration of the rate chamber escape intervals. The ratechamber pace in this situation may thus be termed a safety pace. Forexample, in left ventricle-only synchronized pacing, a right ventricularsafety pace is delivered if the left ventricular pace is inhibited bythe left ventricular protection period and no right ventricular sensehas occurred.

As noted above, synchronized pacing may be applied to multiple sites inthe same or different chambers. The synchronized pacing modes describedabove may be implemented in a multi-site configuration by designatingone sensing/pacing channel as the rate channel for sensing/pacing a ratesite, and designating the other sensing/pacing channels in either thesame or the contralateral chamber as synchronized channels forsensing/pacing one or more synchronized sites. Pacing and sensing in therate channel then follows rate chamber timing rules, while pacing andsensing in the synchronized channels follows synchronized chamber timingrules as described above. The same or different synchronized pacingmodes may be used in each synchronized channel.

4. Intraventricular Interval Display

The present invention relates to a method for displaying electrogramdata received via telemetry by an external programmer or similar devicefrom a pacemaker operating in a cardiac resynchronization mode. Suchdata is displayed in the form of markers representing cardiac eventstogether with interval values indicating the time intervals between suchevents on an electronic display or print output of an externalprogrammer. In such a pacemaker, one heart chamber is paced through arate sensing/pacing channel and another site is paced through asynchronized sensing/pacing channel with the pacing mode being basedupon senses and paces in the rate channel. Markers representing sensingand pacing events are displayed spaced apart in accordance with theirtime sequence, where each marker indicates whether the event is a senseor a pace and in which channel the event occurred. An interval value isdisplayed with each rate channel marker indicating the time intervalbetween the event represented by the marker and the preceding ratechannel event. In alternate embodiments, an interval value is displayedwith each synchronized channel marker indicating the time intervaleither between the event represented by the marker and a nearest ratechannel event or between the event represented by the marker and thenearest preceding rate channel sense or synchronized channel pace.

The invention may be applied to pacemakers in which the rate andsynchronized channels are paired ventricular channels, paired atrialchannels, or a rate channel and a plurality of synchronized channels.FIGS. 2A through 2D show exemplary embodiments of the invention in whichthe pacemaker is operated such that the right ventricle is designatedthe rate chamber and the left ventricle designated the synchronizedchamber. Markers representing ventricular events are displayed withassociated intraventricular intervals. Only ventricular markers andintervals are shown in these examples, but in a typical implementation,markers and intervals for atrial events could also be shown.

FIG. 2A shows an embodiment for a pacemaker operating in a biventricularpacing mode. Timelines are displayed representing electogram data forthe right and left ventricular sensing/pacing channels, labeled RV andLV, respectively. Underneath the timelines are two lines of markersoutput by the display for both ventricular channels. Each marker in thetop line represents right ventricular events, and each marker in thebottom line represents left ventricular events. Associated with eachmarker is an intraventricular interval which indicates the time intervalbetween the event represented by the marker and another ventricularevent. The interval displayed with each right and left ventricularmarker is the interval from the previous right ventricular event.

FIG. 2B shows an example of a display for a pacemaker operating in aleft ventricular-only pacing mode based upon right ventricular senses.The interval displayed with each marker in this case is the intervalfrom the nearest right ventricular sense or left ventricular pace. Thus,if there is no right ventricular sensing present, the interval displayedwith each left ventricular marker is the interval from the previous leftventricular pace.

FIG. 2C shows another scheme in which the interval displayed with eachleft ventricular marker is the interval between the left ventricularevent and the nearest right ventricular event. The nearest rightventricular event may precede or follow the left ventricular event asindicated by a positive or negative interval value, respectively. Theinterval displayed with the right ventricular marker in this embodimentis the interval from the preceding right ventricular event.

FIG. 2D is an alternative approach in which the interval displayed witheach left ventricular marker is the absolute value of the intervalbetween the left ventricular event and the nearest right ventricularevent which may precede or follow the left ventricular event, and theinterval is displayed in alignment with the marker representing thelater of either the left ventricular or right ventricular event. Theinterval displayed with the right ventricular marker is again theinterval from the preceding right ventricular event.

Although the invention has been described in conjunction with theforegoing specific embodiment, many alternatives, variations, andmodifications will be apparent to those of ordinary skill in the art.Such alternatives, variations, and modifications are intended to fallwithin the scope of the following appended claims.

1. A cardiac rhythm management system, comprising: a pacemaker having arate sensing/pacing channel and a synchronized sensing/pacing channel, acontroller for controlling the delivery of paces in accordance with apacing mode based upon rate channel events, and a telemetry interfacefor transmitting signals representing rate and synchronized channelevents; an external programmer with an associated electronic display orprint output, wherein the programmer is configured to receive thesignals transmitted by the pacemaker and output markers representingsensing and pacing events on the display spaced in accordance with theirtime sequence, wherein each marker indicates whether the event is asense or a pace and in which channel the event occurred; and, whereinthe external programmer is configured to display an interval value witheach rate channel marker indicating the time interval between the eventrepresented by the marker and the preceding rate channel event, anddisplay an interval value with each synchronized channel markerindicating the time interval between the event represented by the markerand a nearest rate channel event.
 2. The system of claim 1 wherein therate and synchronized channels are right and left ventricular channels.3. The system of claim 1 wherein the rate and synchronized channels areright and left atrial channels.
 4. The system of claim 1 wherein thepacemaker is operated with a plurality of synchronized channels andfurther comprising displaying markers for each such channel.
 5. Thesystem of claim 1 wherein the displayed interval value with eachsynchronized channel marker indicates the time interval between theevent represented by the marker and the nearest preceding rate channelevent.
 6. The system of claim 1 wherein the displayed interval valuewith each synchronized channel marker indicates the time intervalbetween the event represented by the marker and the nearest rate channelevent which may follow or precede the synchronized channel event asindicated by a negative or positive interval value, respectively.
 7. Thesystem of claim 1 wherein the displayed interval value with eachsynchronized channel marker indicates the absolute value of the timeinterval between the event represented by the marker and the nearestrate channel event which may precede or follow the synchronized channelevent, and the synchronized channel interval is displayed in alignmentwith the marker representing the later of either the synchronizedchannel or rate channel event.
 8. A cardiac rhythm management system,comprising: a pacemaker having a rate sensing/pacing channel and asynchronized sensing/pacing channel, a controller for controlling thedelivery of paces in accordance with a pacing mode based upon ratechannel events, and a telemetry interface for transmitting signalsrepresenting rate and synchronized channel events; an externalprogrammer with an associated electronic display or print output,wherein the programmer is configured to receive the signals transmittedby the pacemaker and output markers representing sensing and pacingevents on the display spaced in accordance with their time sequence,wherein each marker indicates whether the event is a sense or a pace andin which channel the event occurred; and, wherein the externalprogrammer is configured to display an interval value with each ratechannel marker indicating the time interval between the eventrepresented by the marker and the preceding rate channel sense, anddisplay an interval value with each synchronized channel markerindicating the time interval between the event represented by the markerand either the nearest preceding rate channel sense or synchronizedchannel pace, whichever is nearest.
 9. The system of claim 8 wherein therate and synchronized channels are right and left ventricular channels.10. The system of claim 8 wherein the rate and synchronized channels areright and left atrial channels.
 11. The system of claim 8 wherein thepacemaker is operated with a plurality of synchronized channels andfurther comprising displaying markers for each such channel.
 12. Thesystem of claim 8 wherein the displayed interval value with eachsynchronized channel marker indicates the time interval between theevent represented by the marker and the nearest preceding rate channelevent.
 13. The system of claim 8 wherein the displayed interval valuewith each synchronized channel sense marker indicates the time intervalbetween the event represented by the marker and the nearest rate channelsense event or synchronized channel pace event which may follow orprecede the synchronized channel sense event as indicated by a negativeor positive interval value, respectively.
 14. The system of claim 8wherein the displayed interval value with each synchronized channelsense marker indicates the time interval between the event representedby the marker and the nearest rate channel sense event or synchronizedchannel pace event which may precede or follow the synchronized channelsense event, and the synchronized channel sense interval is displayedwith the marker representing the later of either the synchronizedchannel or rate channel event.